1. Field of the Invention
This invention relates to improvements in attachments for use with engine lathes, and, more particularly, to improvements in single point threading apparatuses for use with engine lathes, and still more particularly to improvements in cutting tool and carriage advancement control timing means driven by and synchronized to the rotation of a lead-screw of an engine lathe.
2. Background of the Invention
It has been proposed to provide automatic single point threading apparatuses for use on existing engine lathes. For example, Mackenzie in U.S. Pat. No. 2,903,933 discloses an automatic threading apparatus for use on an existing lathe. The apparatus is mounted, for the most part, on the carriage of the lathe, and is moveable between first and second locations determined by limit switches mounted on the bed of the lathe. A tool carrying block is mounted on the cross slide of the lathe, and includes means for advancing the cutting tool in successively increasing increments with each successive pass. The carriage is driven along the ways of the lathe in ordinary fashion; that is by closing the half-nuts onto the lead-screw. A pneumatic cylinder is attached to the carriage to return it to an initial cutting position.
One of the problems encountered in both manual and automatic operation of engine lathes in single point threading is the timing of the advancement of the cutting tool into the workpiece. Typically, engine lathes are provided with a timing dial which is coupled by a gear directly to the lead-screw, and which includes a hand which is rotated by the rotation of the lead-screw to present a relative reading of the rotation of the lead-screw. Ordinarily, in the manual operation of the lathe, the operator, after adjusting the distance to which the cutting tool will be moved into the workpiece during the cutting operation, manually advances the cutting tool into the turning workpiece. This is done as the needle on the timing dial passes one of the numbers thereon. Depending upon whether even or odd numbered threads are being cut in the workpiece, the operator may advance the cutting tool at any number, or all even or all odd numbers respectively. This manual procedure, however, requires that the engine lathe be operated at relatively slow rotational velocities. Additionally, because of the high degree of operator attention required, this results in operator fatigue after relatively short operating times. On the other hand, with most of the automatic single point threading apparatuses proposed heretofore, no adequate timing mechanism has been employed, except, for example, extremely complicated gearing mechanisms, multi-start clutches, or reversible carriage direction producing means during the cutting process.